MOTION SYSTEM WITH A CONFIGURABLE FEEDFORWARD CONTROL

Abstract

 The present invention relates to a motion system (10) comprising a motion hardware system (100) and a motion control system (200) configured to control the movement of the motion hardware system (100). The hardware system (100) comprises a motion stage (102), a platform (110) supporting the motion stage (102), and a machine frame (116) resting on a ground surface (300). The platform (110) comprises a base (112) and an active vibration isolation system (114) arranged between the base (112) and the machine frame (116). The active vibration isolation system (114) comprises actuators to provide together at least three degrees-of-freedom (DOF) actuation of the base (12). The motion control system (200) comprises a feedforward control (210) comprising a vibration isolation system controller (230) for controlling the at least three DOF actuation of the active vibration isolation system (114) to compensate, by exerting a counteracting force (F) on the base (112), for expected reactions forces exerted by the motion stage (102) on the base (112) when operating. The feedforward control (210) comprises a memory (224) for storing a string of characters defining the motion equations based on the topology of the motion stage (102), and a processing unit (222) for processing said string of characters to compute said counteracting force (F).

Description

Field of the invention

[0001] The present invention relates to a motion system comprising a motion stage for imparting movements to an equipment, in particular a semiconductor processing equipment. The motion stage is mounted on a base resting on an active vibration isolation system. The active vibration isolation system is controlled by a configurable feedforward control to compensate for expected reactions forces exerted by the motion stage on the base when operating.

Background of the invention

[0002] Precision motion systems, in particular semiconductor processing equipment such as positioning devices, coordinate measuring machines or robots, comprise so-called active isolation systems, as disclosed in US6'021'991, for isolating precision motion systems from ground vibration. Active isolation systems typically comprise several active bearings which are assembled between a granite base onto which the precision motion system can be mounted and a machine frame that rests on the floor. Active isolation systems therefore ensure the operation of precision motion systems with as little parasitic movement as possible, as a result of which a high positioning or measurement accuracy is obtained.

[0003] It is known to use feedforward control to compensate for reaction forces generated by precision motion systems. This compensation scheme uses the known stage motions to compute forces and torques to be applied by the actuators to the base to compensate for reaction forces and thus avoid unwanted base motions.

[0004] EP0502578 discloses an example of implementation of a feedforward control in an optical lithographic device with a lens system fastened to a machine frame of the device. The optical lithographic device comprises a motion stage which is situated below the lens system and by means of which an object table is displaceable relative to the lens system over a guide surface of a support member coupled to the motion stage. The optical lithographic device is provided with a force actuator system which is fastened to a reference frame of the device and is controlled by a feedforward control. The force actuator system exerts, during operation, a compensatory force on the machine frame with a direction which is opposed to a direction of a reaction force exerted simultaneously on the support member by the motion stage, and with a value which is substantially equal to a value of the reaction force. The device also includes a feedback damping system to prevent movements of the machine frame caused by forces other than the driving forces exerted by the positioning device on the object table, such as seismic forces transmitted from the ground onto which the optical lithographic device is mounted.

[0005] EP1803969 discloses another motion system comprising a motion stage a feedforward control and a feedback damping system. The feedforward control comprises a control unit adapted for compensating the impact of inertial forces generated by a motion stage. The control unit comprises a memory that contains transfer functions of the moving parts of the motion stage to appropriately filter the quasi-continuous forces to take the motion stage dynamics into account, and a model of the forces that can suddenly occur.

[0006] The feedforward control of the motion system of the prior art described above has the inconvenient to be dependent on the specific topology of the motion stage degrees of freedom. In this respect, EP0502578 discloses a motion stage capable of moving in X and Y directions in a plane, and requiring compensation of in-plane reaction forces, whereas EP1803969 discloses a motion stage with only one degree of freedom. There is however a great variety of motion stage topologies with different types and numbers of degrees of freedom. The computation of the counteracting forces to be compensated based on the motion stage movements is performed inside the feedforward control, using motion equations. These must be adapted for each type of motion stage topology to compute the counteracting forces.

[0007] This computation of counteracting forces based on motion stage topology implies programming and compilation of programing languages that cannot be done on site. In the event of a change in motion stage topology during development phase, a new program for the feedforward control would therefore need to be compiled, which is cumbersome and slow. In addition, to support different motion stage topologies, the motion system would need to store a library of different programs to execute motion equations corresponding to each topology, whereby none of these programs can be removed from the library to avoid breaking backward compatibility. Over time, maintaining a library with many obsolete entries can become a serious burden and incur costs.

Brief summary of the invention

[0008] An aim of the present invention is therefore to provide a motion system with a feedforward control that can be easily adapted to the specific topology of a motion stage.

[0009] Another aim of the present invention is to provide a motion system which can be adapted for any new motion stage topology directly on-site.

[0010] These aims are achieved notably by a motion system comprising a hardware system and a motion control system configured to control the movement of the hardware system. The hardware system comprises a motion stage, a platform supporting the motion stage, and a machine frame resting on a ground surface. The platform comprises a base and an active vibration isolation system arranged between the base and the machine frame. The active vibration isolation system comprises actuators to provide together at least three degrees-of-freedom (DOF) actuation of the base. The motion control system comprises a feedforward control comprising a vibration isolation system controller for controlling the at least three DOF actuation of the active vibration isolation system to compensate, by exerting a counteracting force on the base, for expected reactions forces exerted by the motion stage on the base when operating. The feedforward control comprises a memory for storing a string of characters inputted by an operator and defining the motion equations based on the topology of the motion stage, and a processing unit for processing said string of characters to compute said counteracting force.

[0011] In an embodiment, the motion control system further comprises at least one position controller configured to acquire position and acceleration of a motion axis of the motion stage, a master controller and a digital bus. The master controller is configured to receive and process data relative to the position and acceleration of the motion axis of the motion stage corresponding to the motion equations. The digital bus connects the at least one position controller to the master controller and the latter to the active vibration isolation system controller. The master controller is configured to compute in real-time the counteracting forces based on the string of characters and to send the computed counteracting forces to the active vibration isolation system controller.

[0012] In an embodiment, the master controller is configured to provide a user interface to edit the stored string of characters.

[0013] In an embodiment, the user interface is connected to the master controller through a wired or wireless network.

[0014] In an embodiment, the user interface comprises a computer, a portable computer, a tablet, a smartphone and/or a touch screen.

[0015] In an embodiment, the motion system further comprises another memory, for example a hard drive, for storing predetermined strings of characters defining the motion equations of the motion stage corresponding to different topologies of the motion stage, which can be selected using a dedicated software.

[0016] In an embodiment, the string of characters contains mathematical expressions for equations in the following form

wherein

F = (F_X,F_y,F_z,T_x,T_y,T_z)^T is the vector of said counteracting forces in at least three DOF

x,

are the vectors of respectively motion stage axes positions and accelerations p is a vector of tunable parameters, and

f is a function defining the motion equations for the given motion stage topology.

[0017] In an embodiment, tunable parameters comprise items representing a mass, a dimension, an angular momentum and/or an inertia.

[0018] In an embodiment, the motion control system is configured to provide a user interface to edit the values of said tunable parameters.

[0019] In an embodiment, the motion system further comprises sensors in the active vibration isolation system to provide together three or six DOF measurements of the motions of the base, and a damping controller for controlling said three or six DOF actuator of the active vibration isolation system based on the sensors' outputs to dampen any vibrations caused for example by seismic forces transmitted from said ground surface.

[0020] In an embodiment, the tuning of the vector of tunable parameters p is performed by executing a grid search tuning by varying one or more items of said vector of tunable parameters to find a set of parameters allowing to reduce an energy of an output signal generated by said damping controller.

[0021] In an embodiment, the tuning of the vector of said tunable parameters p is performed by a software by executing a model-based sensitivity analysis tuning of said vector of tunable parameters based on derivatives of the motion equations allowing to reduce an energy of an output signal generated by said damping controller.

[0022] The invention will be better understood with the aid of the description of several embodiments given by way of examples and illustrated by the figures, in which:

• Figure 1 shows a block diagram of the motion system comprising a motion hardware system and a motion control system adapted to control the hardware system as a function of the expected movements of the motion stage.
• Figure 2 shows a schematic view of the motion system of Figure 1 comprising a motion stage of a first topology,
• Figure 3 shows a block diagram of a feedforward control and a feedback damping system of the motion control system of Figure 2, and
• Figure 4 shows a schematic view of the motion hardware system similar to the hardware system of Figure 2 comprising a motion stage with another topology.

Detailed description of several embodiments of the invention

[0023] With reference to Figure 1, the motion system 10 comprises a motion hardware system 100 and a motion control system 200 configured to control the motion stage 102 of the hardware system 100 and to compensate the expected reactions forces exerted by the motion stage 102 on the base 112 by controlling through a digital bus 260 an active vibration isolation system 114.

[0024] Referring to Figure 2, the motion hardware system 100 comprises a motion stage 102 of a specific topology, a support assembly 110 supporting the motion stage 102 and a machine frame 116 holding the support assembly 110 and resting on a ground surface 300. The support assembly 110 comprises the base 112, for example a granite slab, and the active vibration isolation system 114 mounted between the base 112 and the machine frame 116.

[0025] A stationary part of the motion stage 102 is fixed to the base 112. The active vibration isolation system 114 comprises actuators (not shown) to provide together at least three degrees-of-freedom (DOF) actuation of the base 112. In the illustrated embodiment of Figure 2, the motion stage 102 comprises a first and a second linear motion axes 103a, 103b arranged to move their carriage along to two orthogonal axes x, y in the coordinate system x, y, z. In the embodiment of Figure 2, the second linear motion axis 103b is stacked on the first linear motion axis 103a, by being attached to the carriage of the first linear motion axis 103a. Therefore, when a motion is performed with the first linear motion axis 103a, the moving mass is the sum of the mass of the carriage of the first linear motion axis 103a and the total mass of the second linear motion axis 103b. The motion equations must take this into account to compute the counteracting forces. If the topology was inverted, with the first linear motion axis 103a being stacked on the second linear motion axis 103b, it would require different motion equations corresponding to this topology.

[0026] With reference to Figure 3, the motion control system comprises a feedforward control 210 comprising a vibration isolation system controller 230 for controlling the at least three DOF actuation of the active vibration isolation system 114 to compensate, by exerting a counteracting force F on the base 112, for expected reactions forces exerted by the movement of the first and second linear motion axis 103a, 103b of the motion stage 102 on the base 112 when the motion stage 102 is under operation to move an equipment, in particular a semiconductor processing equipment to a specific position, thereby providing an accurate positioning system insensible to the reaction forces generated by the motion stage on the base.

[0027] The feedforward control 210 comprises a memory 224 for storing a string of characters defining the motion equations based on the topology of the motion stage 102, and a processing unit 222 for processing the string of characters to compute the counteracting force vector F.

[0028] Advantageously, the string of characters determining the counteracting force vector F does not need to be provided in a particular programming language as it does not need to be compiled prior to its use. This feature allows an important level of flexibility regarding the topologies of the motion stage.

[0029] In an embodiment, a user may provide a text file containing the string of characters to be interpreted by the processing unit 222 to compute the counteracting force F.

[0030] In an embodiment, a user may use a graphical programming language or graphical system modelling to generate the string of characters to be interpreted by the processing unit 222 to compute the counteracting force F.

[0031] Referring to Figure 2, the motion control system comprises a first and a second position controller 250a, 250b of the motion stage 102. The second position controller 250b is configured to drive the first linear motion axis 103a along the y axis and to acquire position y and acceleration ÿ of the movements of its carriage to which the second linear motion axis 103b is attached. The first position controller 250a is configured to drive the second linear motion axis 103b along the x axis and to acquire position x and acceleration ẍ of the movements of its carriage. The motion control system 200 further comprises a master controller 220 and a digital bus 260 connecting the first and second position controllers 250a, 250b to the master controller 220 and the master controller 220 to the active vibration isolation system controller 230.

[0032] The master controller 220 is configured to receive and process data relative to the position x, y and acceleration ẍ, ÿ of the first and second linear motion axes 103a, 103b of the motion stage 102 when operating using the digital bus 260 as transmission means and according to the string of characters to compute the counteracting force vector F. The computational power of the master controller 220 allows the interpretation of the string of characters to derive mathematical expressions and a sequence of mathematical operations every time the string of characters is modified by the user. The computational power of the master controller 220 also allows the computation of the counteracting force vector F in near real-time using the said sequence of mathematical operations. The computed counteracting force vector F is transmitted to the active vibration isolation system controller 230 using the digital bus 260 to control the actuators of the support assembly 110 of the motion hardware stage 100 to counteract the reactions forces generated by the motion stage.

[0033] Advantageously, the master controller 220 comprises a user interface allowing an operator to enter and/or edit the motion equations determining the counteracting force F. In an embodiment, the user interface allows a user to enter strings of characters corresponding to the topology of the motion stage.

[0034] In an embodiment, the user interface may be integrated in the master controller or connected to the master controller via a wired network. Alternatively, the user interface may be connected to the master controller via a wireless network, allowing its use from a remote device.

[0035] The user interface may for example be a simple bus for data transfer such as a USB port allowing the user to transfer a file containing the string of characters. Alternatively or complementarily, the user interface may include means for the user to directly enter (write) the string of characters into the master controller 220. The user interface may include a computer, a remotely connected computer, a tablet, a smartphone or any other such type of electronic device allowing to share data with the master controller.

[0036] The first and second position controllers 250a, 250b comprise each a delayed circuit to delay the signal, by a few milliseconds, for driving the first and second linear motion axes 103a, 103b of the motion stage 102 in order to take into consideration the computing time of the master controller and the digital bus latency. This ensures that actuators of the active vibration isolation system 114 are controlled by the active vibration isolation system controller 230 in synchronization with the reactions forces exerted by the motion stage 102 on the base 112.

[0037] In an advantageous embodiment, the active vibration isolation system 114 further comprises inertial sensors, for example seismic sensors (not shown) to provide together three or six DOF measurements of the motions of the base 112. The support assembly comprises a feedback damping system 240 transmitting measurements from the inertial sensors to a damping controller 245 for controlling, at each sampling period, the actuators of the active vibration isolation system 114 based on the inertial sensors' outputs to dampen any vibrations caused for example by seismic forces transmitted from the ground surface 300. The force vector output of damping controller 245 is added to the computed counteracting force F and used as force reference for the actuators (not shown) that provide at least three degrees-of-freedom (DOF) actuation of the base 112. The motion system 10 can therefore counteract the reaction forces of the motion stage while being isolated from vibrations from the ground surface 300.

[0038] The string of characters may be retrieved from a configuration file which may comprise a configurable set of motion equations corresponding to different predefined motion stage topologies. This file may be downloaded in the memory 224 of the master controller 220.

[0039] The equations used by the master controller 220 to compute the counteracting force F can be expressed

, wherein

F = (F_X,F_y,F_z,T_x,T_y,T_z)^T is the vector of the counteracting forces in at least three DOF

x,

are the vectors of respectively motion stage axes positions and accelerations p is a vector of tunable parameters, and

f is a function defining the motion equations for the given motion stage topology.

[0040] The motion equations are given in the form of at least three expressions for calculating, at each sampling period, the three forces F_X,F_y,F_z, and three torques T_x,T_y,T_z, for a 6DOF system to compensate for the motion stage reaction forces. The calculation of the forces uses Newton's second law of motion F = m · a and its equivalent for rotary motions. The expressions for the values of torque may include gravity compensation to maintain the base horizontal when the motion stage moves in the plane.

[0041] The vector of tunable parameters p comprises items representing a mass, a dimension such as a length, a width, a height, a diameter, an angular momentum an inertia of the motion stage. Any other relevant physical quantity for the determination of the counteracting force F can be included in the vector of tunable parameters.

[0042] The motion control system may provide a user interface to edit the values of these tunable parameters.

[0043] One or more parameters of the vector of tunable parameters p can be tuned using a dedicated software to increase the performances of the control motion system. The string of characters can be provided to the software, allowing an evaluation of the equations determining the counteracting force which makes possible to run parameter-tuning experiments.

[0044] In an embodiment, a grid search parameter tuning can be performed by the software so as to optimize one or more parameters simultaneously. Typically, a couple of parameters (p,p') of the vector of tunable parameters p are to be tuned simultaneously. For each pair of test parameters (p_i,p_j'), a stage motion of the motion stage is repeated. For each experiment, the motion of the base 112 is measured. A dimension reduction algorithm such as a PCA (Principal Component Analysis) can then be used to define a cost function. The minimum of this cost function provides the best couple of parameters which can then be used to compute the counteracting force F. The cost function can be defined as the energy of an output signal generated by said damping controller.

[0045] In another embodiment, a model-based sensitivity analysis tuning is performed allowing a fast-converging tuning scheme. Here, the expression model-based means that the analysis takes into account the particular motion equations corresponding to the topology of the motion stage and therefore the counteracting force to be applied. Referring to figure 3, the lower part comprising the damping controller 245 and the support assembly 110 can be well approximated by a linear system. Moreover, the motion stage dynamics can usually be modelled with high accuracy as all components may be chosen and defined by a user. Therefore, the transfer function from the counteracting force F to the measurement output Q(t,p) can be modelled and simulated using a dedicated software. The upper part, that is the feed-forward control 210 which is responsible for computing the counteracting force F can be non-linear.

[0046] The model-based sensitivity analysis relies on an estimation of the variation of Q with respect to the parameters p_i forming the vector of tunable parameters p around a given starting point. In other words, the partial derivatives of Q with respect to p are estimated around a measurement signal. Then, an update of the components of p are computed so as to reduce the cost function derived from the signal Q. This method is based on the well-established theory of online parameter tuning, optimal control, repetitive control and iterative learning control.

[0047] Alternatively or complementarily, a delay tuning to compensate for communication-bus transmission time and/or various accumulated phase-delay within the whole control loop can be applied.

[0048] In an embodiment, this delay to be applied is considered as one additional parameter τ for every motion stage axis. The sensitivity is defined as the variation of the output signal Q with respect to this parameter τ and can be estimated by finite differences using an additional measurement performed with a slightly different stage delay. This approach can be used in conjunction with both the described tuning techniques.

[0049] Figure 4 shows a motion hardware system 100 with a motion stage 102 with a different topology having three degrees-of-freedom, i.e., two orthogonal linear movements along the axes x, y and one rotational movement about the axis z . This level of flexibility in defining the motion equations allows for the compensation of the reaction forces of virtually any topology of motion stage mounted on the support assembly 110. The motion stage may be stacked linear and rotary systems, parallel kinematics systems, systems with arbitrary number of degrees-of-freedom, etc.

[0050] In more complex examples, the user may introduce intermediate temporary variables to reduce the overall number of operations. The above motion equations, which correspond to a rigid-body model of the motion stage, could be extended with some internal dynamics of input or output filters, thereby covering more in-details modelling of the motion stage and motion stage control.

Reference list

[0051] 

Motion system 10

Motion hardware system 100

Motion stage 102
First and second linear motion axes 103a, 103b

Support assembly 110

Base 112 (e.g. granite slab)

Active vibration isolation system 114

Machine frame 116

Motion control system 200

Feedforward control 210

Master controller 220

Processing unit 222

Memory 224

Vibration isolation system controller 230

Feedback damping system 240

Damping controller 245

Position controllers 250a, 250b
Delay timer 252

Digital bus 260

Ground surface 300

Claims

1. Motion system (10) comprising a motion hardware system (100) and a motion control system (200) configured to control the movement of the motion hardware system (100), said motion hardware system (100) comprising a motion stage (102), a support assembly (110) supporting the motion stage (102), a machine frame (116) resting on a ground surface (300), wherein the support assembly (110) comprises a base (112) and an active vibration isolation system (114) arranged between the base (112) and the machine frame (116), said active vibration isolation system (114) comprising actuators to provide together at least three degrees-of-freedom (DOF) actuation of the base (112), the motion control system (200) comprising a feedforward control (210) comprising a vibration isolation system controller (230) for controlling said at least three DOF actuation of the active vibration isolation system (114) to compensate, by exerting a counteracting force (F) on the base (112), for expected reactions forces exerted by the motion stage (102) on the base (112) when operating, characterized in that said feedforward control (210) comprises a memory (224) for storing a string of characters defining the motion equations based on the topology of the motion stage (102), and a processing unit (222) for processing said string of characters to compute said counteracting force (F).

2. Motion system (10) of claim 1, wherein the motion control system (200) further comprises at least one position controller (250a, 250b) configured to acquire position (x; y) and acceleration (ẍ,ÿ) of a motion axis of the motion stage (102), a master controller (220) configured to receive and process data relative to the position (x; y) and acceleration (ẍ,ÿ) of the motion axis of the motion stage (102) corresponding to said motion equations and a digital bus (260) linking said at least one position controller (250a, 250b) to the master controller (220) and said master controller (220) to the active vibration isolation system controller (230), wherein the master controller (220) is configured to compute in real-time the counteracting force (F) based on said string of characters and to send the computed counteracting forces (F) to the active vibration isolation system controller (230).

3. Motion system (10) of the preceding claim, wherein the master controller (220) is configured to provide a user interface to enter and/or edit the stored string of characters.

4. Motion system (10) of the preceding claim, wherein said user interface is connected to the master controller through a wired or wireless network.

5. Motion system (10) of claim 3 or 4, wherein said user interface comprises a computer, a portable computer, a tablet, a smartphone and/or a touch screen.

6. Motion system (10) of any of the claims 2 to 5, further comprising another memory for storing predetermined strings of characters defining the motion equations of said motion stage (102) corresponding to different topologies of the motion stage, which can be selected using a dedicated software.

7. Motion system (10) of any preceding claim, wherein said string of characters contains mathematical expressions for equations in the following form

wherein

F = (F_X,F_y,F_z,T_x,T_y,T_z)^T is the vector of said counteracting forces in at least three DOF

x,

are the vectors of respectively motion stage axes positions and accelerations p is a vector of tunable parameters, and

f is a function defining the motion equations for the given motion stage topology.

8. Motion system (10) of the preceding claim, wherein said vector of tunable parameters (p) comprises components representing a mass, a dimension, an angular momentum and/or an inertia.

9. Motion system (10) of claims 7 or 8, wherein the motion control system (200) is configured to provide a user interface to edit the values of said vector of tunable parameters (p).

10. Motion system (10) of any of claims 7 to 9, further comprising sensors in the active vibration isolation system (114) to provide together three or six DOF measurements of the motions of the base (112), and a feedback damping system (240) comprising a damping controller (245) for controlling said three or six DOF actuator of the active vibration isolation system (114) based on the sensors' outputs to dampen any vibrations caused by seismic forces transmitted from said ground surface (300).

11. Motion system (10) of claim 10, wherein the tuning of said vector of tunable parameters (p) is performed by a software executing a grid search tuning of said vector of tunable parameters to find a set of parameters allowing to reduce an energy of an output signal generated by said damping controller (245).

12. Motion system (10) of claim 10, wherein the tuning of said vector of tunable parameters (p) is performed by a software executing a model-based sensitivity analysis tuning of said vector of tunable parameters based on derivatives of the motion equations allowing to reduce an energy of an output signal generated by said damping controller (245).

Drawing